The invention disclosed herein pertains to a scroll sign module comprised of two rolls that are mounted between laterally spaced apart side walls of a frame for rotating bidirectionally about parallel axes to wind an information bearing web onto one roll as the web unwinds from the other roll such that information can be read from the web segment that extends from one roll to the other.
Roll sign modules have various applications. A popular application is to display the price of vehicle fuel where several modules are arranged in juxtaposition to compose the price and are mounted on a pole at a great height adjacent a highway for being visualized by vehicle drivers at a great distance. A typical roll sign module has one or two electric motors operatively coupled in driving relation with the two spaced apart rolls by means of a suitable mechanism including gears, chains, sprockets, toothed belts and pulleys. Typically, at least one of the rolls in a pair is coupled to a driving source inelastically or positively and the other roll in the pair is a so-called web tensioning roll that is driven rotationally through the agency of an elastic device such as a helical or a spiral spring. The spring that is coupled to the tension roll provides for maintaining a substantially constant tension in the web even though the diameter of one roll increases and the other decreases as the web is wound and unwound from one roll to another.
U.S. Pat. No. 734,982, which was granted to Smith on Jul. 28, 1903, discloses a scroll sign module wherein a tension roll is journaled for rotation on a rotationally driven shaft. A spiral spring is installed in a cylindrical recess in the end of the tension roll concentrically to the roll driving shaft that extends through the recess. The inside end of the spiral spring is attached to the rotationally driven shaft and the outside end of the spring is attached to the tension roll so that when the shaft rotates the tension roll is driven elastically by way of the spiral spring that couples the shaft to the roll. The shafts for the tension roll and the other cooperating roll are provided with sprockets for being driven with a motor and a closed loop chain. In this patent, the drive mechanism includes a lead screw operated with a chain and gear system to switch the take-up roll to becoming the unwind roll for the web and, vice versa, when the end of the web is reached.
Among the problems of driving rolls with chains and sprockets is that these components must be lubricated regularly to maintain good module operation and inhibit corrosion. Applying lubricant to the components of a sign that is mounted on a tall structure, as is usually the case, is an inconvenient and unpleasant task. Chains also have the undesirable property of becoming less flexible when the ambient temperature drops to below 0.degree. on the Fahrenheit scale, which is not uncommon during the winter in the northern states. A stiff chain requires a greater force to bend it around the sprockets which can result in overloading the small module operating motor. A loose chain may come off the sprocket and an excessively tight chain may impose a greater load on the motor that drives a module.
U.S. Pat. No. 4,773,176, which was granted to Grehan on Sep. 27, 1988, also drives a tension roll in a sign module through the agency of a spiral spring. In this design a toothed pulley fits on the end of the tension roll shaft. The pulley has a large axial counter bore in which the spiral spring is positioned concentrically to the shaft with the inside end of the spiral spring attached to the shaft and the outside end attached to the toothed pulley. Driving the pulley rotationally causes an elastic or yieldable torsional force to be applied to the shaft for the roll so the shaft and roll can change their angular relationship to compensate for the overall change in the diameter of the roll and the web thereon that results from the amount of web on one roll decreasing while it is increasing on the other roll.
One problem with driving through the agency of a toothed belt is that thermal expansion differs substantially from the thermal expansion of the metal frame that supports the components of the module. Hence, at low ambient temperatures, the toothed belt becomes too loose and at higher temperatures the belt may become too tight. An excessively tight belt can impose a large radial load on the motor and the bearing for the roll and a loose belt can unmesh from the toothed pulleys. Moreover, in cold weather toothed belts become stiffer and require increased force to bend around the pulleys. This also imposes a greater load on the motor which could make the module inoperative at some temperatures.
U.S. Pat. No. 3,255,541, which was granted to Bettcher on Jun. 14, 1966, discloses another version of a scroll module. In this patent a web tension maintaining roll has stub-axles extending axially inwardly for a short distance at opposite ends of the roll. The stub-axle at the driven end of the roll extends coaxially from a pinion gear that is driven by a motor driven gear chain. A helical spring is mounted concentrically to the stub-axle inside of the tension roll. One end of the helical spring is attached to the power driven stub-axle and the other end of the spring is attached to the roll to thereby provide an elastic connection between the power driven stub-axle and the roll to compensate for the changing overall diameter of the web on the roll as the web is transferred between the parallel arranged tension and cooperating rolls. The Bettcher module would have the problems incident to driving rolls through gear, sprocket and chain systems as has been explained.
U.S. Pat. No. 5,673,504, which was granted to Brown on Oct. 7, 1997, also discloses a module wherein a tension roll is driven elastically through the agency of a spiral spring that is positioned inside of the tension roll as in the previously mentioned Smith patent. In this patented design a module is comprised of the usual laterally spaced apart side frame members between which the two parallel web winding and unwinding rolls are positioned. To provide for rotation of the tension roll, bearing members are fixedly mounted in each of the spaced apart frame members in coaxial relationship. Each bearing member has a central bore constituting an inside bearing or bushing for an axle and has a smooth concentric periphery constituting an outside bearing on which an end cap for the roll can rotate. The end cap has an annular recess for containing a spiral spring that is concentric to the rotational axis of the roll. A pulley for driving the roll rotationally with a belt is positioned outside of the frame member and a stub-axle that is unitary with the pulley extends axially from it for being journaled in the bushing and for extending into the spring recess in the end cap to provide for connecting the inside end of the spiral spring to the rotationally driven stub-axle and the outside end of the spiral spring to the end cap. Since the end cap is latched to the roll, when the stub-axle is driven rotationally by means of the belt and pulley, a torsional force is applied to the end cap through the spring for rotating the tension roll.
Additional patent references that disclose driving a tension roll in a module through the agency of a helical spring are U.S. Pat. No. 4,110,925 which was granted to Strand et al. on Sep. 5, 1978 and U.S. Pat. No. 1,902,884 which was granted to Wagner on Mar. 28, 1933.